1. Field of the Invention
The present invention relates to a magnetic recording medium capable of high-density recording and, more particularly, to a magnetic recording medium suitable for flexible discs, magnetic tapes or hard discs and a preparing method thereof.
2. Description of the Prior Art
Hitherto, a Co-Cr alloy film, a partially oxidized film of cobalt, a partially oxidized film of Fe-Co alloy or the like have been proposed as a perpendicular magnetic recording medium capable of high-density magnetic recording. Such partially oxidized films have a high perpendicular magnetic anisotropy, are capable of high-density recording and have a high resistance to sliding of the head. Such partially oxidized films are obtainable by vapor deposition in an oxygen atmosphere or by reactive sputtering, also in an oxygen atmosphere.
As a recording-reproducing head for the perpendicular magnetic recording medium, there have been proposed heads of main magnetic exciting type and of ring type. Unlike the former, the latter has an advantage in that a relatively high reproduction output is obtainable even if it is provided with only a perpendicularly magnetized film without any soft magnetic underlayer such as permalloy and is, therefore, highly effective.
There are, however, problems in that if recording is made on a single layer of perpendicularly magnetized film and reproduction of the recorded information is made, the waveform is bound to the double-humped, and therefore, the reproduced output in the low-density region is bound to be low. Another problem is that the perpendicular magnetic recording medium comprising a film of partially oxidized cobalt is low in reproduction output compared with the medium comprising a film of Co-Cr alloy.
Meanwhile, there is a problem that a system representing a combination of a perpendicular magnetic recording media comprising films of partially oxidized Fe-Co alloy and partially oxidized cobalt with a ring type head is lower in reproduction output than that comprising the Co-Cr alloy film. To be noted particularly is that if the perpendicular magnetic anisotropy is raised for an increased recording density, it is bound to result in a decrease of the reproduction output. That is, if recording is made on a single layer of Co-Cr medium and the recorded information is reproduced by an Mn-Zn ferrite head, a standardized output of approximately 100 .mu.Vo-p/mm/(m/sec)/turn is expected, that of the partially oxidized Fe-Co alloy medium is only 50 .mu.Vo-p/mm/(m/sec) turn or so.
In order to overcome these problems, a method for providing as an underlayer a film of Fe-Co alloy or the like having magnetic anisotropy oriented in an in-plane direction has been proposed. Such a method, though largely increasing the reproduction output and the recording density, is not yet sufficient in respect of S/N ratio, overwrite property and the like.